Autoregulation is the ability of a vascular bed to maintain blood flow despite changes in perfusion pressure. For a long time it had been assumed that the choroid is a strictly passive vascular bed, which shows no autoregulation. However, recently several groups have identified some autoregulatory capacity of the human choroid. In the brain and the retina the mechanism behind autoregulation is most likely linked to changes in transmural pressure. In this model arterioles change their vascular tone depending on the pressure inside the vessel and outside the vessel. In the choroid, several observations argue against a direct involvement of arterioles. However, the mechanism behind choroidal autoregulation remains unclear.

In the present study autoregulation of the choroid will be investigated during a decrease in ocular perfusion pressure, which will be achieved by an increase in intraocular pressure. Pressure/flow relationships will be investigated in the absence or presence of a NO synthase inhibitor. As a control substance the alpha-receptor agonist phenylephrine will be used.

he IOP will be raised by a 11 mm diameter, standardized suction cup placed on the temporal sclera with the anterior edge at least 1 mm from the limbus.

Procedure: Laser Doppler flowmetry

Measurement of choroidal blood flow

Procedure: Measurement of intraocular pressure

Placebo Comparator: 3

Physiologic saline solution

Procedure: Suction cup application

he IOP will be raised by a 11 mm diameter, standardized suction cup placed on the temporal sclera with the anterior edge at least 1 mm from the limbus.

Procedure: Laser Doppler flowmetry

Measurement of choroidal blood flow

Procedure: Measurement of intraocular pressure

Eligibility

Ages Eligible for Study:

19 Years to 35 Years

Genders Eligible for Study:

Male

Accepts Healthy Volunteers:

Yes

Criteria

Inclusion Criteria:

Men aged between 19 and 35 years, nonsmokers

Body mass index between 15th and 85th percentile (Must et al. 1991)

Normal findings in the medical history and physical examination unless the investigator considers an abnormality to be clinically irrelevant

Normal laboratory values unless the investigator considers an abnormality to be clinically irrelevant

Normal ophthalmic findings, ametropia < 3 Dpt.

Exclusion Criteria:

Regular use of medication, abuse of alcoholic beverages, participation in a clinical trial in the 3 weeks preceding the study

Treatment in the previous 3 weeks with any drug

Symptoms of a clinically relevant illness in the 3 weeks before the first study day

History of hypersensitivity to the trial drug or to drugs with a similar chemical structure

History or presence of gastrointestinal, liver or kidney disease, or other conditions known to interfere with, distribution, metabolism or excretion of study drugs

Blood donation during the previous 3 weeks

Contacts and Locations

Choosing to participate in a study is an important personal decision. Talk with your doctor and family members or friends about deciding to join a study.
To learn more about this study, you or your doctor may contact the study research staff using the Contacts provided below.
For general information, see Learn About Clinical Studies.

Please refer to this study by its ClinicalTrials.gov identifier: NCT00810927